(tar)Sparse Files

Dealing with Compressed Archives

Compression

Archiving Sparse Files
----------------------

     *(This message will disappear, once this node revised.)*

   A file is sparse if it contains blocks of zeros whose existance is
recorded, but that have no space allocated on disk.  When you specify
the `--sparse' (`-S') option in conjunction with the `--create' (`-c')
operation, `tar' tests all files for sparseness while archiving.  If
`tar' finds a file to be sparse, it uses a sparse representation of the
file in the archive.
FIXME: xref Creating Archives
   , for more information about creating archives.

   `--sparse' (`-S') is useful when archiving files, such as dbm files,
likely to contain many nulls.  This option dramatically decreases the
amount of space needed to store such an archive.

     *Please Note:* Always use `--sparse' (`-S') when performing file
     system backups, to avoid archiving the expanded forms of files
     stored sparsely in the system.

     Even if your system has no no sparse files currently, some may be
     created in the future.  If you use `--sparse' (`-S') while making
     file system backups as a matter of course, you can be assured the
     archive will always take no more space on the media than the files
     take on disk (otherwise, archiving a disk filled with sparse files
     might take hundreds of tapes).
     FIXME: xref incremental when node name is set.

   `tar' ignores the `--sparse' (`-S') option when reading an archive.

`--sparse'
`-S'
     Files stored sparsely in the file system are represented sparsely
     in the archive.  Use in conjunction with write operations.